This commit moves the storage of bDeformGroup and the active index
to Mesh, Lattice, and bGPdata instead of Object.
As explained in T88951, the list of vertex group names is currently
stored separately per object, even though vertex group data is stored
on the geometry. This tends to complicate code and cause bugs,
especially as geometry is created procedurally and tied less closely
to objects.
The "Copy Vertex Groups to Linked" operator is removed, since they
are stored on the geometry anyway.
This patch leaves the object-level python API for vertex groups in place.
Creating a geometry-level RNA API can be a separate step, the changes
here are invasive enough as it is.